To understand what is happening in the Middle East, you must first understand what is happening in Texas. To understand what is happening there, you should read the resolutions passed at the state's Republican party conventions last month. Take a look, for example, at the decisions made in Harris County, which covers much of Houston.

The delegates began by nodding through a few uncontroversial matters: homosexuality is contrary to the truths ordained by God; "any mechanism to process, license, record, register or monitor the ownership of guns" should be repealed; income tax, inheritance tax, capital gains tax and corporation tax should be abolished; and immigrants should be deterred by electric fences. Thus fortified, they turned to the real issue: the affairs of a small state 7,000 miles away. It was then, according to a participant, that the "screaming and near fist fights" began.

I don't know what the original motion said, but apparently it was "watered down significantly" as a result of the shouting match. The motion they adopted stated that Israel has an undivided claim to Jerusalem and the West Bank, that Arab states should be "pressured" to absorb refugees from Palestine, and that Israel should do whatever it wishes in seeking to eliminate terrorism. Good to see that the extremists didn't prevail then.

But why should all this be of such pressing interest to the people of a state which is seldom celebrated for its fascination with foreign affairs? The explanation is slowly becoming familiar to us, but we still have some difficulty in taking it seriously.

In the United States, several million people have succumbed to an extraordinary delusion. In the 19th century, two immigrant preachers cobbled together a series of unrelated passages from the Bible to create what appears to be a consistent narrative: Jesus will return to Earth when certain preconditions have been met. The first of these was the establishment of a state of Israel. The next involves Israel's occupation of the rest of its "biblical lands" (most of the Middle East), and the rebuilding of the Third Temple on the site now occupied by the Dome of the Rock and al-Aqsa mosques. The legions of the antichrist will then be deployed against Israel, and their war will lead to a final showdown in the valley of Armageddon. The Jews will either burn or convert to Christianity, and the Messiah will return to Earth.

What makes the story so appealing to Christian fundamentalists is that before the big battle begins, all "true believers" (ie those who believe what they believe) will be lifted out of their clothes and wafted up to heaven during an event called the Rapture. Not only do the worthy get to sit at the right hand of God, but they will be able to watch, from the best seats, their political and religious opponents being devoured by boils, sores, locusts and frogs, during the seven years of Tribulation which follow.

The true believers are now seeking to bring all this about. This means staging confrontations at the old temple site (in 2000, three US Christians were deported for trying to blow up the mosques there), sponsoring Jewish settlements in the occupied territories, demanding ever more US support for Israel, and seeking to provoke a final battle with the Muslim world/Axis of Evil/United Nations/ European Union/France or whoever the legions of the antichrist turn out to be.

The believers are convinced that they will soon be rewarded for their efforts. The antichrist is apparently walking among us, in the guise of Kofi Annan, Javier Solana, Yasser Arafat or, more plausibly, Silvio Berlusconi. The Wal-Mart corporation is also a candidate (in my view a very good one), because it wants to radio-tag its stock, thereby exposing humankind to the Mark of the Beast.

By clicking on www.raptureready.com, you can discover how close you might be to flying out of your pyjamas. The infidels among us should take note that the Rapture Index currently stands at 144, just one point below the critical threshold, beyond which the sky will be filled with floating nudists. Beast Government, Wild Weather and Israel are all trading at the maximum five points (the EU is debat ing its constitution, there was a freak hurricane in the south Atlantic, Hamas has sworn to avenge the killing of its leaders), but the second coming is currently being delayed by an unfortunate decline in drug abuse among teenagers and a weak showing by the antichrist (both of which score only two).

We can laugh at these people, but we should not dismiss them. That their beliefs are bonkers does not mean they are marginal. American pollsters believe that 15-18% of US voters belong to churches or movements which subscribe to these teachings. A survey in 1999 suggested that this figure included 33% of Republicans. The best-selling contemporary books in the US are the 12 volumes of the Left Behind series, which provide what is usually described as a "fictionalised" account of the Rapture (this, apparently, distinguishes it from the other one), with plenty of dripping details about what will happen to the rest of us. The people who believe all this don't believe it just a little; for them it is a matter of life eternal and death.

And among them are some of the most powerful men in America. John Ashcroft, the attorney general, is a true believer, so are several prominent senators and the House majority leader, Tom DeLay. Mr DeLay (who is also the co-author of the marvellously named DeLay-Doolittle Amendment, postponing campaign finance reforms) travelled to Israel last year to tell the Knesset that "there is no middle ground, no moderate position worth taking".

So here we have a major political constituency - representing much of the current president's core vote - in the most powerful nation on Earth, which is actively seeking to provoke a new world war. Its members see the invasion of Iraq as a warm-up act, as Revelation (9:14-15) maintains that four angels "which are bound in the great river Euphrates" will be released "to slay the third part of men". They batter down the doors of the White House as soon as its support for Israel wavers: when Bush asked Ariel Sharon to pull his tanks out of Jenin in 2002, he received 100,000 angry emails from Christian fundamentalists, and never mentioned the matter again.

The electoral calculation, crazy as it appears, works like this. Governments stand or fall on domestic issues. For 85% of the US electorate, the Middle East is a foreign issue, and therefore of secondary interest when they enter the polling booth. For 15% of the electorate, the Middle East is not just a domestic matter, it's a personal one: if the president fails to start a conflagration there, his core voters don't get to sit at the right hand of God. Bush, in other words, stands to lose fewer votes by encouraging Israeli aggression than he stands to lose by restraining it. He would be mad to listen to these people. He would also be mad not to.

· George Monbiot's book The Age of Consent: a Manifesto for a New World Order is now published in paperback